Currently it is only possible to save sections as section templates from a project and not from a project template.
But it can be useful if you can save sections as section templates from project templates also.
This idea came from ticket 68953. The customer converted an intake to project but the sections that they needed were lying in project templates. They did not have any section templates.
So I had to tell them to go to all the projects (where there are sections that they need in this newly created project) and save the required sections as section templates, and then create a section group, and then import all these sections to the new project.
My recording below -
https://drive.google.com/file/d/1mSiZbdZCSCp89giFv7qOHQrkKyltN0HF/view?usp=sharing
Call recording with customer -
https://drive.google.com/file/d/1RBignLcvE3LxCiStyiO72nBPUxp16PjL/view?usp=sharing